Board Thread:Pokémon Help/@comment-32347401-20170903011127/@comment-27535813-20170903070842

Bad nature. Run modest or timid instead.

Moveset is not good either, run Psyshock(Psychic works, but this means you can't hit pass special walls), Moonblast, Shadow Ball/Focus Blast/HP Fire(you'll need to get the proper IVs for this), Healing Wish/Will-o-wisp.

Destiny Bond is actually okay, but Gardevoir should usually see itself trying to hit hard as much as it can instead of just dying and sacrificing itself to kill another(which it can otherwise just kill along with its good sp.atk stat). Thus, Healing Wish can work instead if you really want a sacrificial move.

Toxic is actually okay too, but Gardevoir isn't going to be tanking hits and surviving while waiting for opponent to die from Toxic, neither will it auto force switches too, so you might as well run Will-o-Wisp to patch up it's bad defense stat.

Energy Ball is okay if you really want coverage over Ground-types, Water-types and Rock-types, but there isn't much use other than that.

EVs should go 252 EVs to sp.atk, 252 to speed, and 4 to Def/Sp.Def.